I'm not doing this for the money, or for the glory. I do it for myself first, because a song that exists is worth more than an idea left in a corner. And once it exists, it might as well be useful.
That's why tracks are offered for download as they go: the full MP3, and, when it exists, the instrumental version. If a file is still missing, it simply hasn't been uploaded yet — it's coming.
If you want to sing over it, rap over it, slow it down, break it apart, remake it better: go ahead. Drop the SoundCloud link to your version from the song's page. I'll listen, and if it speaks to me, it gets published alongside the original. Nothing to sign, nothing to pay — just the urge to see where it can go.